Background arts concerning methods for supplying powder to an extruder are as follows.
(1) A background art of mixing powder having different particle sizes by a powder stock hopper using an extruder equipped with a powder stock hopper is disclosed (e.g., Patent Document 1).
(2) A background art of providing a material supplying part and a degassing part in an extruder supply hopper and removing a gas in a resin material is disclosed (e.g., Patent Documents 2 and 3).
Background arts of producing a PPE resin composition are as follows.
(3) A background art screw configuration for enhancing PPE powder-conveying ability is disclosed (e.g., Patent Documents 4 and 5).
(4) A background art of degassing volatile components of PPE containing volatile components is disclosed (e.g., Patent Document 6).
(5) A background art for preventing the generation of non-melted PPE in a process for producing PPE concentrate is disclosed (e.g., Patent Document 7).
(6) A background art concerning flame-retarding PPE concentrate pellets where pellet size is 2 to 5 mm and a process for producing a PPE resin composition using the same is disclosed (e.g., Patent Document 8).
(7) A background art of subjecting a flame retardant to a divisional feeding is disclosed (e.g., Patent Document 9).
(8) A background art of regulating the particle size of a PPE concentrate and the amount of fine powder is disclosed (e.g., Patent Document 10).
(9) A background art of regulating the amount of fine powder of a flame-retarding PPE concentrate is disclosed (e.g., Patent Document 11).
(10) A background art, concerning melt-kneading of two kinds of PPE concentrates, of regulating the difference in heat-resisting temperatures between the PPE concentrates within 40° C. or less is disclosed (e.g., Patent Document 12).
Patent Document 1; JP 2000-108120 A
Patent Document 2; JP 11-165341 A
Patent Document 3; JP 08-197609 A
Patent Document 4: JP 09-070872 A
Patent Document 5: JP 10-024483 A
Patent Document 6: U.S. Pat. No. 6,133,379
Patent Document 7: JP 04-117444 A
Patent Document 8: Japanese Patent No. 3,297,523
Patent Document 9: Japanese Patent No. 3,465,969
Patent Document 10: U.S. Pat. No. 6,365,710
Patent Document 11: U.S. Pat. No. 6,096,821
Patent Document 12: JP 2003-246865 A
There are two problems concerning an extrusion processing step for PPE powder.
One is a problem concerning handling of powder. PPE powder contains a lot of fine particles of not more than 100 μm and much gas and, therefore, when it is supplied to a supplying inlet port of an extruder, the conveying ability thereof significantly lowers and productivity greatly lowers. Further, since there are many fine particles in PPE powder, the powder is apt to cause blocking and is retained in a hopper wall or cause blocking in a stock hopper whereby the supply amount lowers or, reversely, it flows at a stroke whereby variations in the supply amount may become large.
The other problem is that the glass transition temperature of PPE is as high as 220° C. and its melt viscosity is also high and, therefore, temperature of a PPE composition for extrusion processing is as high as 300 to 360° C. Accordingly, foreign substances are apt to be generated in an extruder and, further, a rubber in a high-impact polystyrene (hereinafter abbreviated as “HIPS”) is apt to be thermally deteriorated.
In recent years, there has been a demand for a production process which is excellent in productivity, stably supplies PPE powder, is well-balanced in physical properties of thermally deforming temperature and MFR, is suppressed in generation of foreign substances and is capable of impact resistance.
However, the background arts are not sufficient against such problems. The present inventors have already developed a screw mechanism for powder in Patent Documents 4 and 5 and increased the conveying ability of the PPE powder. However, PPE powder contains fine particles of not more than 100 μm in an amount of 5 to 99% by weight. In order to apply it to a producing machine, it is necessary to develop a method for supplying PPE powder that fluidizes powder, and prevents a dust explosion and generation of foreign substances. In order to supply the PPE powder in a stable manner and to enhance the conveying ability, it was found to be important an art where powder is firstly supplied from a temporarily storing hopper to a loss-in-weight feeder for powder, then supplied from the loss-in-weight feeder for powder to an extruder supply hopper and to an extruder whereupon the accompanying gas is removed therefrom.
Concerning the removal of gas from an extruder supply hopper, background arts of dividing the space into a material supplying part and a gas separating part is disclosed in Patent Documents 2 and 3. In these documents it is disclosed that, since gas accompanying the material supplied to the barrel of an extruder flows back from the barrel to the extruder supply hopper, the flown-back gas and supplying material are separated so that a conveying ability is enhanced. However, since PPE powder as addressed in the present invention suffers from a large amount of accompanying gas, there has been a demand for a technique of separating gas before supplying to an extruder barrel and, in addition, removing gas after the PPE powder is melt-kneaded.